Red, purple and blue fruits contain anthocyanins (pronounced an-tho-sy-a-nins), which are potent antioxidants that help to strengthen your immune system. Blueberries are great but can be pricey and you can find the same antioxidant goodness in seasonal purple produce like grapes or eggplants. Orange fruits and veggies contain beta-carotene, which the body uses to make vitamin A, another vital nutrient for immune health. Don’t like carrots? Try sweet potato or pumpkin instead.

All fruits and veggies contain immune boosting vitamin C but leafy green veggies, berries, citrus fruits and capsicums are extra rich. To protect the vitamin C in your foods, eat raw or steam gently and don’t keep produce warm for long periods – heat and oxygen destroy vitamin C. Fresh foods also provide a powerful antioxidant called glutathione (gloot-a-thy-own), which helps strengthen your immune system but it is also quickly destroyed by heat.

Go nuts for Brazil

Brazil nuts are a rich source of the antioxidant mineral selenium, vital to helping the immune system fight off the viruses responsible for colds and flu. Just one or two Brazil nuts each day can provide all the selenium you need. Other good sources include seeds, shellfish, whole grains and lean meats. One animal study suggests that low levels of selenium may cause the flu virus to mutate to a stronger form[i]. Brazil nuts are also high in zinc, another immune booster that works hand-in-hand with vitamin C.

Watch the sweet stuff

Foods that contain refined carbohydrates – such as biscuits, sweets and sugary fizzy drinks – are overloaded with sugar. Although sugar gives you an energy boost, it’s short-lived and soon triggers a sugar low as your body tries desperately to keep blood glucose (blood sugar) levels to within normal limits. Recent research suggests that overloading on sugar actually triggers a reduction in the functioning of the immune system by inhibiting phagocytosis, the process by which viruses and bacteria are chewed up by white blood cells[ii]. That doesn’t mean you have to cut sugar out completely – just moderate what you eat and make it a treat, not a daily staple.

Don’t skimp on slumber

Getting enough restful sleep is vital for mind and body. This is because lack of sleep stresses the body, lowering the immune system and increasing your chances of infection.

One study published by the European Journal of Physiology found that just six days of restricted sleep affected the immune system so much that it reduced the protective effects of a flu vaccination. They also reported that a lack of sleep makes you more susceptible to catching colds[iii].

Get a move on

Staying active, even in the colder months, is vital for many reasons. Exercise boosts immunity by increasing the number of white blood cells, natural killer cells, that fight the invading microorganisms that cause infection.

But exercising needs to be a habit. Don’t think you have to force yourself on a daily hour-long run though – half an hour is plenty or three ten-minute bursts of activity. Aerobic exercise is important for strengthening the heart, lungs and bones while strength exercises, using weights, are important to help build lean muscle. Try yoga for better balance, flexibility, meditation and relaxation. Stress zaps your energy and your immune system, so moving more is more important than you might think.

Exercising outside also means that you’re exposed to sunlight. This reacts with a cholesterol-like substance in the skin to make vitamin D, which is vital for a healthy immune system. One study of children showed that vitamin D could be an important way to avoid flu[iv]. But remember that even in winter it’s important to protect skin from harsh rays by using sun protection. You can also increase your vitamin D levels by eating mushrooms, tofu, eggs, margarine and fatty fish like salmon and fresh tuna.

Pop a probiotic

Your body is alive with microorganisms, which live in synergy with your own body cells. They’re vital for life and produce vitamins and proteins to boost your immune health. Poor diet, medications and stress can all affect your good bacteria levels. So as well as taking a probiotic supplement (probiotic bacteria are also found naturally in foods like sauerkraut and preserved lemons) you can feed the good guys with prebiotic foods such as garlic, onions, leeks and kale.

Get a flu jab

Every year a different strain of flu travels around the world and so a different flu vaccination is offered. The flu vaccine is a dead or inactive form of the virus so it will not make you sick. By having a flu jab, your body is able to fight the infection by making antibodies – disease fighting soldiers – that are specific to that particular strain. And if your body was to come across that strain again, it would be able to react rapidly to make the right flu fighting antibody soldiers. This is because it would already know the specific type of antibodies needed to fight that specific germ.

The flu is a very serious condition. So if you’re in an at risk group or you’re prone to infections, it’s important to get a flu shot. It takes weeks to recover from the flu and your immune system is lowered for weeks afterwards, which increases your chances of catching another infection.